Yori and his twin sister Iku, once incredibly close, have grown apart in recent years, with Yori increasingly distancing himself from her. Unbeknownst to Iku, Yori's aloofness stems from his forbidden love for his sister, a feeling that has left him sleepless and tormented, especially given their shared living arrangements. In an attempt to suppress his desires, Yori has tried to distract himself by pursuing Iku's best friend and even considered attending a boarding school in another city to escape his feelings. However, when Iku begins to discuss her own romantic interests and potential boyfriend, Yori's resolve crumbles, and he confesses his true feelings to her. Iku, who loves her brother dearly and wishes to maintain their close bond, is willing to do whatever it takes to keep them together. Yet, Yori's desire for Iku extends beyond a sibling's affection, and he longs to have her as a lover, not just a sister loyal to her twin.